Field of the Invention
The present invention relates to a method of manufacturing a solid-state image sensor and a solid-state image sensor.
Description of the Related Art
Conventionally, a CCD image sensor, a CMOS image sensor, and the like are known as solid-state image sensors. The CMOS image sensor is superior to the CCD one in terms of power consumption and multi-functionality, and the application range of the CMOS image sensor is expanding recently. A chip used in the CMOS image sensor includes a pixel region including a light receiving portion (photodiode) that generates charges upon irradiation with light, and a peripheral circuit region where charges generated in the pixel region are read out as an electrical signal. The chip used in the image sensor is fabricated by performing dicing in a scribe region (scribe line) provided on a wafer.
In the pixel region, a plurality of pixels are formed. In the pixels, light receiving portions, and transistors for transferring charges generated in the light receiving portions to a peripheral circuit are formed. In the peripheral circuit region, transistors for processing a signal read out from the pixel are formed. Recently, the driving speed of solid-state image sensors is increasing. Along with this, the driving speed of the transistor in the peripheral circuit region also needs to be increased. To meet this request, there is proposed a technique of forming a metal silicide layer (metal semiconductor compound layer) from a compound of Si and a high melting point metal such as Ti or Co on the surface portions of respective regions serving as the gate electrode of the transistor and the electrodes of the source and drain regions.
A solid-state image sensor disclosed in Japanese Patent Laid-Open No. 2008-98373 pertains to a solid-state image sensor in which a silicide layer is formed on an electrode. In order to improve the flatness of the surface of the interlayer insulation film of the solid-state image sensor, the dummy of a gate electrode and the dummy of a protective insulation film are arranged in a scribe region, thereby reducing a global step.
A metal silicide layer is formed by causing silicon and a high melting point metal to react with each other on the surfaces of the source and drain regions. However, silicon and the high melting point metal do not completely react with each other, and the unreacted high melting point metal spreads in the semiconductor at a certain probability, causing metal contamination. This may cause characteristic degradation of the image sensor, such as a white defect. In the technique disclosed in Japanese Patent Laid-Open No. 2008-98373, silicon is exposed at most part of the scribe region. Considering that a general scribe region has a width of about 50 μm to 200 μm, a layer of a large amount of metal silicide is formed in the scribe region when forming a metal silicide layer. As a result, a large amount of unreacted high melting point metal is generated in the scribe region and spreads. Even if an insulating film covers the pixel region, the metal spreads in the insulating film and reaches the surface of a silicon wafer. This causes characteristic degradation of the image sensor, such as a white defect.